src: use MallocedBuffer abstraction for buffers

Drop `Free` and `std::unique_ptr` in favor of Node's `MallocedBuffer`
for `char[]` buffer memory mangement.

PR-URL: https://github.com/nodejs/node/pull/23543


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>